The present invention relates to a control method for a construction machine, such as a hydraulic excavator, a backhoe or a loader, and a control device used for said method. More particularly, the invention concerns a control method and a control device which enable an operator who is replacing a front attachment, such as a bucket, that is mounted on the front part of a hydraulic excavator or the like with another attachment, such as a hammer, to set such conditions as hydraulic pressure to be supplied, flow rate and so forth with a single action according to the specific requirements of the selected attachment.
As shown in FIG. 6, a hydraulic excavator typically includes a machine body 1 which comprises a lower structure 1a, an upper structure 1b, a cab 1c, a boom 1d of the front working part and an arm 1e and is adapted to permit a bucket attached to the front part of the shovel to be easily replaced by a different working attachment 2 (for example, a hammer) so that the excavator may be used for various kinds of operation.
As these working attachments 2 are all hydraulic actuators in one way or another and require their own respective working conditions, i.e. rated supply pressures and flow rates of working fluid, it is necessary to set different control criteria for each attachment at hydraulic sources of the main body 1 of the construction machine. For example, even in case of working attachments 2 of the identical type, rated supply pressure and flow rate differ depending on the manufacturer and the capacity of the attachment, and the optimum working conditions for each attachment differ accordingly.
FIG. 7 shows a conventional control device for a hydraulic excavator, which includes hydraulic pumps 4,5 adapted to feed working fluid through a control valve 3 to a working attachment 2 removably attached to the machine body 1. Discharge flow rates of the hydraulic pumps 4,5 are controlled based on engine speed and preset pump outputs, said engine speed adjusted by an accelerator actuator 7 of a diesel engine 6 in accordance with the position of the accelerator, and the preset pump outputs adjusted by pump regulators 8,9.
A flow control valve 10 is disposed at the downstream side of a center bypass line of the control valve 3, with the pressure signal line at its upstream side connected to the pump regulators 8,9. With the configuration as above, the control valve 10 is adapted to conduct what is generally called negative flow rate control, wherein pump flow rate is low when the pressure is high, while pump flow rate is high when the pressure is low. The connection at this part is omitted in FIG. 7.
The accelerator actuator 7 and the pump regulators 8,9 perform the control function in accordance with signals output from a controller 11 which is a part of the machine body 1. The pump regulators 8,9 perform control by way of transforming current to hydraulic pressures by using proportional control solenoid valves 12,13.
As shown in FIG. 7, a typical conventional control method calls for connecting resisters 14a, 14b to a battery 15, the resisters 14a, 14b being capable of coping with various rated pressures and flow rates of working attachments 2.
Then, through a manually operated selector switch 16, electrical signals (electric current in this case) is input into the proportional control solenoid valves 12,13, which transform the current into hydraulic pressures, and the hydraulic pressures are then respectively input into the pump regulators 8,9 adapted to set the outputs of the pumps. Receiving the discharge pressure from the pumps, the pump regulators 8,9 so control the power fed from the engine 6 to the hydraulic pumps 4,5 as to be maintained at a constant level. Thus, the working fluid discharged by the hydraulic pumps 4,5 enables any working attachment 2 mounted on the machine body 1 to function in the rated operating condition.
A conventional control method calls for an operator of a machine such as a hydraulic excavator to adjust the revolution speed of the engine 6 by means of manual operation of an accelerator dial 17. In other words, while signals from the accelerator dial 17 are input to the controller 11 the revolution speed of the engine 6 is detected by a sensor 18 so that signals representing the detected speed are also input to the controller 11.
At that stage, upon comparison of the engine speed set by the accelerator dial 17 with the actual engine speed input from the sensor 18,the controller 11 computes values for driving the accelerator actuator 7 in order to make the actual engine speed consistent with the set speed and outputs the signals that represent the computed values to the accelerator actuator 7.
When the accelerator is operated at its maximum capacity, with the engine speed at the rated value or more, the controller 11 outputs signals to increase the pump outputs so that hydraulic pressure signals which have been transformed at the proportional control solenoid valves 12,13 are input into the pump regulators 8,9. On the other hand, when the engine speed becomes lower than the rated value, the controller outputs signals that will reduce the pump outputs, thereby controlling the outputs of the hydraulic pumps 4,5 not to exceed the engine output.
In addition to a control valve 3 for controlling actions of a working attachment 2, a control valve 3a for controlling actions of another hydraulic actuator, such as a boom cylinder 2a or the like, is disposed on the discharge line of the hydraulic pumps 4,5. These control valves 3,3a are pilot-operated by means of, for example, a pedal-type operating device 19 and a lever-type operating device 19a respectively.